The Earth, magnets, and electrical currents generate magnetic fields. Magnetoresistive (MR) sensors are magnetic sensors that are sensitive to the magnetic field. The MR sensors typically have a thin strip of ferromagnetic material, such as a nickel-iron alloy (also known as Permalloy), through which a current is passed. In the presence of the magnetic field, the thin strip changes resistance, which causes a voltage measured across the thin strip to change.
A magnetic linear sensor is one example of the MR sensor. The linear sensor typically has a magnetic axis that provides a reference point with respect to which a sense of the magnetic field is detected. The sense of the magnetic field is an indication of whether the magnetic field is in a direction along the magnetic axis of the linear sensor, in which case the linear sensor is said to detect a positive sense, or in a direction opposite to the magnetic axis of the linear sensor, in which case the linear sensor is said to detect a negative sense. The positive sense may be the north pole of the magnetic field, and the negative sense may be the south pole of the magnetic field, but other arrangements are also possible. The linear sensor will output a voltage indicative of the sense of the magnetic field.
A magnetic angular sensor is another example of an MR sensor. The angular sensor typically has two magnetic axes arranged at a forty-five degree angle between each other that cooperatively provide a reference point with respect to which an angular position of the magnetic field is detected. The angular sensor will output a voltage indicative of the angular position of the magnetic field, up to a range of 180-degrees.
In addition to the linear sensor and angular sensor, MR sensors that are capable of detecting 360-degrees of rotation are desirable. Such MR sensors can be used for many rotary applications, such as for control of an automobile steering wheel. Therefore, it would be desirable to have a 360-degree MR rotary position sensor that is robust and highly accurate.